Apple boss Steve Jobs has taken a medical leave of absence to focus on his health.
He will remain CEO and be involved in major strategic decisions, but the day-to-day running of the company is now COO Tim Cook's concern.
In an email sent to all Apple employees, the 55-year-old CEO said: "I have asked Tim Cook to be responsible for all of Apple's day to day operations. I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011.
"I love Apple so much and hope to be back as soon as I can.
"In the meantime, my family and I would deeply appreciate respect for our privacy."
In January 2009 Jobs announced a six month leave of absence to allow him to better focus on his health. Cook, who had previously acted as CEO during a 2004 absence, became acting CEO. Jobs underwent a liver transplant in April 2009.
Apple is responsible for the iPhone, iPod touch and iPad devices.